This invention relates to X-ray imaging techniques, and, more particularly, to computerized tomography X-ray imaging using data combined from different scan paths.
Computerized tomography (CT) uses a source of imaging energy such as X-ray energy and a detector for detecting imaging energy that has passed through an object of interest, often a patient being imaged for medical purposes. Typically, a single point source is used with an area detector such as an X-ray detector array.
Relative movement between the source, object of interest, and detector is used to collect data for image reconstruction purposes.
The advent of area X-ray detectors permits measurement of a 2 dimensional data set for each source position, since the detector lies in a 2 dimensional plane. Therefore, it is possible to measure a 1+2=3 dimensional data set of line integrals of the object being imaged.
This dimensional count is encouraging for volumetric imaging such as CT because the imaged object lies in three spatial dimensions. More specifically, complete CT data for a family of parallel planes constitutes a 2+1=3 dimensional data set and completely determines the imaged object.
Unfortunately, cone beam data generated by a single point source does not permit such simple reconstruction. A single circular trajectory does not provide a complete data set for Radon reconstruction (i.e., apart from measurement and discretization errors). Therefore, various scan trajectories have been used.
Generally, the scan trajectories result from relative movement among the source, detector, and object being imaged. Usually, the source is moved in a path about the object to define the scan trajectory. The object being imaged is often a medical patient, but could also be an industrial part being imaged to locate possible defects. Regardless of whether the object being imaged is a patient or an industrial part, the scan trajectory may be defined at least partly by movement of the object relative to the source or relative to the detector.
It has been long known that exact three dimensional (3D) reconstruction of a scanned object requires that any plane intersecting the object must also intersect the scanning path. Therefore, a planar orbit such as the circular orbit with its inherent simplicity and rotational symmetry is not sufficient to provide exact 3D reconstruction.
In order to provide exact 3D reconstruction, scan trajectories use more than one scan path for imaging a given object. A scan trajectory often uses two scan paths, a circular scan path and a complementary scan path. A linear path orthogonal to the plane of the circular scan path is a common scan path used to complement the circular scan path. Another scan paths used to complement a first circular scan path is a second circular orbit tilted relative to the first circular orbit.
Such scan trajectories that provide complete cone beam data may present a number of problems. The imaging often requires highly sophisticated, time-consuming algorithms. Noise and artifacts often result from techniques using interpolation in Radon space.